Check out this photo taken near Aberdeen:
http://www.railphotoprints.co.uk/index/detail/3671/D6141-D6156-CoveBay-1065-RPCBR105.jpg.html
The DVD "Steam on the Speyside Line" by On-line DVD has archive footage from the GNSR and features rare film of a class 21 (ironically given the title of DVD) - the DVD is available from The Strathspey Railway